Piston rod packing lubricator



Aug. 39, 1949. ow

PISTON ROD PACKING LUBRICATOR Filed Nov. 23, 1945 IN V EN TOR. AR THU]? L DOW ATTORNEY Patented Aug. 30, 1949 PISTON ROD PACKING LUBRICATOR I Arthur L. Dow, Easion, Conn, assignor to United Aircraft Corporation, East Hartford, Coma, a corporation of Delaware Application November 28, 1945, Serial No. 630,444

Claims.

This invention relates to hydraulic struts of the type used in aircraft and particularly to improvements in lubrication of the piston rods of such I struts.

Hydraulic struts used in aircraft, for example,

2 retractable landing gear or for moving various control surfaces. A piston rod l4 extends through an axial aperture 16 in the cap 12 and terminates in a piston l8 within the cylinder. The cap l2 5 has an annular flange 20 surrounding the passage to operate retractable landing gear, are provided 66 which 15 provided with an axial recess, or with a metallic, usually bronze, annular wiper groove, 22 in which the usual annular bronze ring which is loosely mounted at the outermost wiper ring 24 is loosely received, this ringt being end of the cylinder cap but which has its inner slightly smaller in diameter than the bot om of diameter fitted to the piston rod for a tight sliding the groove. The cap I2 has an annular flange 26 fit thereon. The function of this wiper ring is to formed by an annular groove in the passage I6 remove any dust or other dirt which may have and in the groove behind it a resilient locking accumulated on the piston rod during the period ring 28 is disposed which holds thie wiper ring 24 it has been withdrawn from the cylinder as the loosely against displacemen in he recess, the rod is returned to the cylinder. Unfortunately ring 24 being in elTect floating in groove 22. in removing dust and other foreign particles from While the outer diameter of ring 24 is somewhat the surface of the piston rod, the wiper ring also smaller than the diameter of recess 22, its internal removes the film of lubricating oil on the piston diameter is such that it has a tight sliding fit rod surface so that the rod is dry as it passes on the external surface of the piston rod l through the cylinder cap into the cylinder and The ring 24 is further provided with a feather the rubber O ring packing seal in the cylinder wiping edge 30 which in a usual manner enables cap cleaves to the dry piston rod surface. This this ring to remov: all ioreigr; partitciles from the sticking of the rubber packing to the piston rod surface of the pis on rod as he la er is moved surface prevents elncient operation of the strut, into the cylinder. greatly shortens the life of the packing and fre- 25 An 0 ring packing 32 of rubber or rubber-like quently causes an immediatetlealru. d t material is also provided in a suitable groove 35 It is -O j Of this inven 0 0 DrOVi 6 all in the passage l6 adjacent the inner wall of the magiclubgicititon of tire surface of hydrgutlilc $111311 cap which provides the hydraulic seal between pis o p s e w e w per r e an e the piston rod and the cap for preventing leakring packing as the piston rod returns into the 3 age of the high pressure fluid in the cylinder cylmden v through passage is around the piston rod l4.

Another obJect of the nvention 15 to prov1de The groove 35 has a depth which is Slightly improved automatlc q j p f the plston less than the circular cross section of the rubber rods of hydraulic struts utlllzmg 011 under presring so that the latter is Somewhat sure hem w1th1 n ihe cgrlllmder oft the strut. 11 35 ressed between the bottom .of the groove and further g efmven g i the piston rod 14. The width of the groove 35, f gfi z z fiz cons rue Ion an Opera Ion 0 however, is somewhat greater than the cross These and other objects and advantages of the sectlor. of 0' rmg so that the a result of reciprocating movement of the rod is caused invention w1ll be apparent from the followmg deto roll along the bottom of the recess, thus protailed description of two embodiments of the min ab nefi lkne di a ti t th ubber invention which have been shown for purposes V g 8 01a ng c o of illustration in the accompanying drawings. fi zg 1 g pi gs ggz g :332:3

In these drawings,

Fig. 1 is a perspective view of the cap and the lubnczaatmg 5 plston rod li between i H n he piston rod of a hydrauhc strut havmg the 1mrmg and he 0 rmg pac mg 32 upon proved lubricating means between the wiper ring 'T t ll l g Of 3 1? DlStOn 3 the 331 3? and the O ring packing I o is en an o ique passage prov1 e in Fig. 2 is an enlarged sectional view of a portion t D :1 me end 2% vvhug terminates agathi of the cap of Fig. 1; and inner en 0 groove or e wiper ring a Fig. 3isaview similar to Fig.2showingamodithe surface of piston rod [4 and the opposite fled construction. end of which extends into the cylinder and is in In Fig. 1, ill represents the hydraulic cylinder communication with the high pressure fluid in and i2 represents the cap of a hydraulic strut the cap end of the cylinder. The passage 36 is commonly used in aircraft, e. g. for operating small in diameter, being only large enough to permit free passage of lubricating oil to groove 22. At its inner end the passage 35 is provided with a counterbore 31 to receive a flow restricting plug, or pellet, 33 the inner end of which is subjected to the high pressure fluid in the cylinder l whenever fluid is admitted to chamber 40 to return the piston rod to the cylinder.

The pellet 38 may be formed of various substances, the only requirements being that it be inert and that it have a porous structure such that it allows only a limited, predetermined quantity of oil to pass through it prevailing in the cylinder. For example, the plug may be made of a powdered metallic substance which has been compressed to a predetermined density, the degree of compression being determined by the nature and fineness .of the material and the pressure of lubricating oil to which it is to be subjected and to some extent the viscosity of the oil used in the strut.

The porosity of the metallic pellet 38 is so designed that the oil admitted under pressure to the cylinder ill on the cap side of the piston penetrates through the pores of this pellet very slightly but sufliciently to discharge enough oil into the groove 22 to spread a very thin film of lubricating oil on the piston rod surface which has been wiped dry by the ring 24 before this surface engages the 0 ring 32. It will be understood that the quantity of oil which reaches the surface of the piston rod is only sufiicient to provide a very thin surface film of lubricant to the piston rod during the In stroke of the latter when the rod surface is dry, and this only when actuating hydraulic fluid is admitted -to the cap side of the piston, the pressure of oil on the surface of pellet 38 on the Out stroke of the piston being negligible and not sufiicient to force oil through the very minute pores in the pellet 33. For example, if the hydraulic pressure admitted to the cylinder for the retraction of a landing gear strut were of the order of 1,000 p. s. i., the plug 38 would be designed for such astrut sothat with this pressure acting on the exposed end of the plug 38 the-oil transmitted through the pores of the metal will be just sufficient to lubricate the piston rod and prevent sticking of the 0" ring to therod.

In Fig. 3, a somewhat modified construction has been shown which has advantages in some installations. In this form of the invention the recess 22 is made somewhat deeper in order to accommodate an annular oil absorbent washer 42 between the wiper ring 24 and the inner end wall.

of the recess. The oil passage 36 in this construction communicates with the bottom of recess 22. Otherwise the construction is similar to that shown in Figs. 1 and 2. The washer 42 can be of felt or any oil absorbent material having sufficient resiliency to discharge its absorbed oil upon compression of the material.

It will be evident that oil which is discharged through passage 36 during the piston stroke in which the chamber 40 is under pressure will be absorbed by the washer 42 which spreads an even film of lubricant on the piston rod l4 as the latter moves inwardly, the washer being pressed firmly against the inner end wall of the recess 22 and against the rod during this movement by ring 24 which compresses the material of the washer as a result of its frictional engagement with rod l4.

On the outward stroke of the piston rod when no discharge of lubricant is desired, the washer is under no pressure and is relatively dry.

It will be understood that a plurality of pasunder the pressure sages 36 may be provided about the periphery of passage i6, each with its flow controlling pellet 38, if desired.

It will be evident that as a result of this invention a very simple and efficient means has been provided for automatically lubricating the surface of a hydraulic piston rod by which the critical problem of sticking of the 0" ring packing to the piston rod surface has been entirely eliminated. It will further be evident that this automatic lubrication has been accomplished by the utilization of oil under pressure available within the hydraulic cylinder of the strut but this only during the piston stroke when lubrication is desired with the result that servicing of the packing in such hydraulic struts has been greatly simplified and the operation of these struts has been greatly improved.

While two embodiments of the invention have been shown and described which are at present preferred embodiments, it will be understood that various changes in the construction and arrangement of the parts may be made without departing from the scope of the invention as defined in the following claims.

What I desire to secure by U. S. Letters Patent is as follows:

1. A hydraulic strut including a cylinder adapted to contain oil under pressure, said cylinder having a cylinder wall and a piston rod reciprocable in a passage in said wall, a packing between said wall and rod for sealing said passage, a wiper ring carried by said wall having a wipin engagement with the surface of said rod as the latter moves into the cylinder prior to its engagement with said packing-a duct in said wall discharging into said passage between said ring and said packing and communicating with said cylinder, and a pellet of porous material in said duct for limiting the flow of oil to said passage.

2. A hydraulic strut including a cylinder adapted to contain oil under pressure, said cylinder having a cylinder cap and a piston rod reciprocable in a passage in said cap, a fluidtight packing between said cap and rod for sealing said passage around said rod, wiping means carried by said cap for wiping the surface of said rod as the latter moves into the cylinder prior to its engagement with said packing, a duct in said cap discharging at its outer end into said passage between said wiping means and said packing and communicating at its inner end with the cylinder, said duct having an enlargement at its inner end, and a mass of porous material in said enlargement for limiting the flow of oil through said duct.

3. A combination as defined in claim 2, in which the porous mass comprises a pellet of powdered metal compressed to have a predetermined density.

4. A hydraulic strut including a cylinder adapted to contain oil under pressure, said cylinder having a cylinder cap and a piston rod reciprocable in a passage in said cap, a fluidtight packing between said cap and rod for sealing said passage around said rod, a recess in the wall of said passage adjacent the outer end thereof, a washer of absorbent material disposed in the inner end of-said recess adjacent said packing having a wiping engagement with the surface of said rod, a wiper ring disposed in said recess abutting said washer having a wiping fit on the surface of said rod, a duct in said cap for supplying fluid from the cylinder to said washer, and means in said duct for limiting the quantity of oil supplied to said washer.

5. A hydraulic strut including a cylinder adapted to contain fluid under pressure, said cylinder having a cylinder cap and a piston rod reciprocable in a passage in said cap, a fluid-tight packing between said cap and rod for sealing said passage around said rod, an annular recess in said passage surrounding said rod, 9. body of absorbent material in said recess, a wiper ring slidable in said recess having a frictional wiping engagement with the surface of said rod which moves said ring into pressure engagement with said body of absorbent material during the movement of 15 said rod into the cylinder, and means for supplying a predetermined limited amount of fluid from the hydraulic cylinder to said body of absorbent 10 Number ARTHUR L. DOW.

summons crmn The following references are oi record in the die or this patent:

Um'mn sums PATENTS Name Date 1,010,498 Hultgren Dec. 5, 1911 1,687,780 Meale Oct. 16, 1928 1,992,746 Fortune Feb. 26. 1935 2,368,137 Harmon Jan. 30. 1945 Product Engineering. Feb. 1945, page 103. (Copy in Div. 52 286-26411). v 

